For this and other reasons, Smith’s new circular chart made many microwave engineering problems in circuits as well as in transmission lines easy to solve graphically (that is, without doing a lot of math).

In 1936, he had the idea of using a circular chart and transforming the reflections mathematically so that no matter how large they were, the numbers would all fit inside the circular boundary of the chart. Fleming for telephone lines, but he kept getting numbers that went off the top and bottom of the chart.

Smith tried to graph the effects of these reflections on an early type of rectangular chart developed by J. These reflected waves can bounce back and forth along the line and are eventually lost, reducing the amount of power transmitted. However, with many types of antennas, some of the waves are reflected back into the line. Ideally, all the waves would go smoothly along the line in one direction and no reflections would occur. Smith originally designed his chart to solve problems he encountered in transmitting radio waves along a special type of cable called a transmission line that conducts the waves from a radio transmitter to an antenna. The microwave engineer’s objective in many instances is to get as much microwave power as possible through electrical obstacles on its way to the goal of being transmitted from an antenna or being amplified in a receiver. This simplified version of a Smith Chart shows both resistance in ohms (numbers on the horizontal axis that range from 0.2 to 10) and the angle of a quantity called the reflection coefficient, in degrees on the outer edge of the circle. From the beginning of World War II until the development of digital computers for engineering problems, the Smith Chart was the dominant tool for microwave engineers. The Chart known as the Smith Chart was the work of Philip Smith and Mizuhashi Tosaku, who seem to have developed it independently of each other.

Smith chart z pdf